Desenvolvimento de fotocatalisadores solares à base de ferro e nióbio para remoção de compostos orgânicos em águas e efluentes

Abstract

The present study aimed at the development of Fe/Nb-based solar photocatalysts for the degradation of contaminants of emerging concerning from water and wastewater in large scale. In the first stage, 10 photocatalysts were synthesized using different synthesis routes. One of these materials (photocatalyst R2-A) was distinctive considering an innovation pertaining to the conventional co-precipitation method. Among all of the materials developed, R2-A achieved 55% global removal of methylene blue, a model compound used for experiments under artificial UVAVis irradiation, thus being one of the strongest candidates for solar photocatalysis. Indeed, under solar irradiation, the effectiveness of R2-A increased up to 95%. Variations between the performances of the photocatalysts under UVA-Vis irradiation compared to solar irradiation were linked to differences on the spectrum of each light source. The association between the different synthesis methods, characterization and photocalytic activity during degradation assays showed expressive correlations between the applied route and the composition, morphology, texture, and optical properties of each material with the photocatalytic performance. In the second stage of this study, the aim was to enhance the performance of materials developed during stage one by pelletizing photocatalysts using bohemite gel as a binding agent. Enhanced activity was confirmed by testing the degradation of a contaminant of emerging concern. However, the change in the target compound and in the operational conditions revealed a new perspective related to the photocatalytic process. Among the five pelletized materials, one of the photocatalysts which initially showed low efficiency (photocatalyst C4-B) achieved the best performance in an optimum load of 1 g·L -1 , reaching more than 40% degradation of carbendazim within the first 15 minutes of reaction. This result was associated to the classical oxidative mechanism (via HO radicals) and low adsorption rate, which was not favored by the pH. Pelletized photocatalyst showed resistance and efficiency in three different reaction cycles with some decay in performance after each cycle. The repeatability test confirmed the viability of all of the pellets produced with negligible mass deviation after the resistance test. Although, some changes in the characteristics of the material were noticed and led to a decrease in its performance. The concept of photocatalytic space-time yield was adopted as a benchmark for the comparison of each photo reactor used for the degradation of carbendazim and demonstrated higher yield for the semi-pilot solar reactor, followed by the solar simulator and the bench scale reactor (UVA-Vis). Results obtained in this study guided to some remarks considering the challenges to be faced by photocatalysis